1. Field of the Invention:
The field of invention relates to portable jigsaws, sometimes called "saber saws." These saws are used to make straight or curved cuts, particularly in wood, plywood, hard board and laminates. The saws are used, for instance, to rip, cross-cut, bevel, miter, and make interior cuts. Saber saws consist essentially of a portable, hand-held, electric motor which is gear-connected to a reciprocating element which supports the blade. The blade is a thin, flat metal strip and has teeth along a long edge. The blade reciprocates longitudinally.
The invention relates to the blade, and particularly to the teeth on the blade.
2. Description of the Prior Art:
Prior art saber saw blades are well known and extensively used. The blades vary in length from, for instance, 21/2" to 4" or more. They are used extensively for cutting wood, plywood, hard wood, laminates and the like.
A portable, hand-held electric motor drives the blade in a reciprocating fashion up to, for instance, 3200 strokes per minute with a stroke length of, for instance, approximately 7/8". The saws are generally operated in a manner whereby the blade extends transversely, or perpendicularly, through the material being sawed, wherein the material extends in a horizontal plane and the blade extends in a vertical plane and reciprocates therein.
In operation, the saw blade reciprocates while the saw is being held and forced into the particular cut it is making the wood. Generally, the plane of the wood extends horizontally and the saw is held vertically while cutting the wood. The teeth conventionally extend forward of the operator when the saw is used and pushed forward by the operator. The teeth of the saw are such that the saw cuts only on the return movement of the blade as the blade reciprocates longitudinally upwardly toward the saw. As the blade reciprocates downwardly, o away from the saw motor, there is relatively little cutting action, since the teeth are designed specifically to cut on the upward or return stroke.
Several problems exist with respect to such prior art blades:
(1) A primary problem is that the prior art saber saw cutting action is grossly inefficient. The cutting action occurs only on one-half of the reciprocating strokes; namely, the upward stroke, and virtually all cutting is lost on the downward stroke. Much time and energy is lost in such cutting action, since the downward stroke is wasted.
(2) A further problem is that the blade gets dull not from cutting the wood, but from the non-cutting, inefficient, downward stroke. The blade heats up from friction on the downward stroke, when the teeth are dragged under pressure across the wood. The blade is continuously being pushed against the wood in the cutting direction by the operator who does not distinguish in applying pressure between the upward and downward movements of the reciprocating blade. Movement is so rapid that selective pressure is impossible. The friction creates heat in the teeth, eventually causing the blade to lose its temper, and to develop dull rounded points. These dull points in turn produce more friction and heat, causing the teeth to become even more dull.
(3) Another problem is that blades are used up relatively rapidly. Since the blades are generally originally tempered and relatively hard, it is extremely difficult for the average work man to sharpen the blade by refiling. The blade is generally thrown away.
(4) Another problem is the relatively ragged finished cut that results from the blade action. The teeth on the prior art saber blade have a hook form, with the hooks pointed in an upward direction. These hook teeth exert a chiseling action on the upward stroke, ripping the fibers of the wood. Adequate force is available from the saw motor to overcome fiber resistance, and when necessary, the fibers are even torn and the wood splintered to accomplish the cutting effect. Such ragged cut is particularly prevalent when a crosscut is being made.
(5) A further problem is that the saw itself, and particularly the motor is being intermittantly loaded on the upward stroke and unloaded on the downward stroke, resulting in uneven and harmful loading on the saw motor. Additionally, unwanted vibration occurs.
(6) Since virtually all cutting takes place on an upward stroke, most of the sawdust from the cutting process is moved upwardly and deposited on the working surface of the board. This obscures the guidelines to a point where the operation of sawing must be periodically stopped and sawdust blown away either mechanically or manually.
In summary, we have a blade in the prior art which is inefficient since it only cuts on one-half of its reciprocation, which creates friction on the downward stroke where there is very little cutting, causing the blade to dull and be discarded, which has a relatively rough tearing action in its cut, and which deposits most of the sawdust on the line of the cut.